Disk drive device provided with fluid dynamic bearing

ABSTRACT

A sleeve supports a shaft. A housing member is arranged so as to surround the sleeve and make the end of the sleeve protrude. A base member holds the housing member and fixes a stator core so as to surround the housing member. A hub drives a recording disk by being rotated integrally with the shaft, with a magnet being fixed to an annular portion concentric with the shaft so as to face the stator core fixed to the base member. A thrust member is rotated integrally with the hub, and a descender portion and a ring portion.

CROSS-REFERENCE TO RELATED APPLICATIONS

This is a Divisional Application based on U.S. Ser. No. 13/530,344,filed on Jun. 22, 2012, which is a Divisional of U.S. Ser. No.12/576,179, filed on Oct. 8, 2009, which is based upon and claims thebenefit of priority from the prior Japanese Patent Application No.2009-020953, filed on Jan. 30, 2009, and Japanese Patent Application No.2009-020954, filed on Jan. 30, 2009, the entire contents of which areincorporated herein by reference.

FIELD OF THE INVENTION

The present invention relates to a disk drive device, and in particular,to a disk drive device provided with a fluid dynamic bearing.

DESCRIPTION OF THE RELATED ART

Recently, a disk drive device such as a Hard Disk Drive (HDD) has beendramatically improved in its rotational accuracy by providing a fluiddynamic bearing, allowing the device with high density and largecapacity. Due to this, a disk drive device provided with a fluid dynamicbearing has been mounted in a wide variety of apparatuses. Accordingly,the disk drive device has been used in various environments. Inparticular, the device has been increasingly mounted in portabledevices, also called mobile devices, and with this, the disk drivedevice has been required to have improved impact resistance in order towithstand impacts when dropped, etc. On the other hand, the mobiledevices have been, year by year, smaller in size, thinner in thickness,lighter in weight and larger in capacity; and for further realizingthese characteristics, it is required that each component composing adisk drive device is further smaller in size and thinner in thickness,and a material for the component is lower in density. As a result, theimpact resistant performance thereof is deteriorated, creating atrade-off requirement.

For example, considering the use of the disk drive device in a desk toppersonal computer, the impact exerted on the disk drive device isapproximately 100 G at most, and therefore, when the disk drive devicewithstands an impact of approximate 300 G as a maximum impact for ashort time, for example, 1 ms, there rarely occurs a failure inpractical use. However, considering impact situations in the presentmobile devices, there may occur a failure in practical use, if the diskdrive device does not withstand 800 G as the maximum impact for a shorttime, for example, 1 ms. To deal with this, an annular convex areasandwiched between a flange portion of a sleeve and one end surface of asleeve holder, is formed inside a tubular inner trunk portion. Alubricant is filled between the annular convex area and the flangeportion as well as between the annular convex area and the sleeve holder(for example, Japanese Patent Application Publication No. 2008-92790,Japanese Patent Application Publication No. 2007-198555 and JapanesePatent Application Publication No. 2004-270820).

With the increasing use of the mobile devices, the impact resistance isrequired to be further improved. Under such circumstances, the presentinventors have made it cleat that the disk drive device is required towithstand even 1300 G or more as the maximum impact for a short time,for example, 1 ms, in order not to cause any failure in practical use.In particular, the disk drive device provided with a fluid dynamicbearing is configured such that fixed bodies and rotating bodies faceeach other in several narrow gaps, and hence an impact affects all thesenarrow gaps. Accordingly, there occur many types of failures due to theimpact, requiring comprehensive technical innovation to be developedbecause those cannot be solved by a single technical innovation.Further, the inventors have intensively studied on the influence by astrong impact occurring when dropped, etc., on the disk drive device, atthe level of components, thereby acquiring the following classificationfor the types of failures.

A first type of failures occurs due to deformation of a componentitself. When an impact acceleration is applied to the disk drive device,a stress occurs in accordance with the mass of the component. When thestress exceeds the elastic limit of the component, deformation occurs.In the disk drive device into which the fluid dynamic bearing or thelike is accurately incorporated so as to be slightly spaced apart, thedeformation of the component causes a malfunction in the entire diskdrive device. A second type thereof occurs due to the deformation of ajoint portion between a plurality of components. The joint portion islikely to cause stress concentration and has a low strength incomparison with that of the integral portion, and therefore deformationor destruction by a stress due to an impact acceleration occurs, causingthe disk drive device to be in a malfunction.

A third type thereof occurs due to scattering of the lubricant filledbetween the rotating body and the fixed body, by the impact occurringwhen dropped, etc. In the disk drive device provided with the fluiddynamic bearing, the rotating body is supported by a dynamic pressuregenerated in the lubricant, making sufficient presence of the lubricantindispensable. However, scattering of the lubricant by the impactacceleration causes shortage of the lubricant, thereby the disk drivedevice being in a malfunction such as burn-in of a bearing, in a shorttime. A fourth type thereof occurs due to temporary elastic deformationof a component. For example, part of components of the fixed bodiesdeforms in the elastic region by a stress due to an impact acceleration,and thereby the part thereof is scraped due to a contact with part ofcomponents of the rotating bodies, even for a short time, causingscraped powder, etc. The scraped powder enters the gap of the fluiddynamic bearing and promotes the wearing thereof, causing the fluiddynamic bearing to be in a malfunction such as burn-in of a bearing in ashort time. In order to improve the impact resistance of the disk drivedevice such that the device withstands 1300 G or more as the maximumimpact for a short time, for example, 1 ms, the disk has tocomprehensively deal with all of the aforementioned four types offailures; however, dealing with the third type thereof is particularlyeffective.

SUMMARY OF THE INVENTION

The present invention has been made in view of these circumstances, anda purpose of the invention is to provide a technique in which the impactresistance against an impact when dropped, etc., is improved.

In order to solve the aforementioned problems, a disk drive deviceaccording to an embodiment of the present invention comprises: a tubularsleeve that supports a shaft; a tubular housing member that is arrangedso as to surround the sleeve and make the end of the sleeve protrude; abase member that holds the housing member and fixes a stator core so asto surround the housing member; a hub that drives a recording disk bybeing rotated integrally with the shaft, with a magnet being fixed to anannular portion concentric with the shaft so as to face the stator corefixed to the base member; and a tubular thrust member that is rotatedintegrally with the hub. The sleeve has a flange extending in the outerdiameter direction at the hub side edge, and forms a first annular areabetween the flange and the hub side edge of the housing member; the basemember forms a second annular area on the outer circumference side ofthe housing member; the thrust member has a ring portion that surroundsthe sleeve and a descender portion that surrounds the housing member,where the ring portion is fixed, with an adhesive, to the interior wallof a hub side tubular wall formed in the hub, and is rotated in thefirst area, and where the descender portion is joined to the outer edgeportion of the ring portion and fixed, with an adhesive, to the interiorwall of the hub side tubular wall, and is rotated in the second area;and a lubricant is filled between the housing member and the thrustmember, and also between the flange of the sleeve and the hub.

According to the embodiment, because the thrust member has the descenderportion in addition to the ring portion, the fixing area with the hubcan be enlarged and the capacity of a capillary seal can be enlarged,allowing the impact resistance to be improved.

The base side edge of the descender portion of the thrust member may beformed so as to more protrude than that of the hub side tubular wall. Inthis case, because the adhesive is suppressed from entering thecapillary seal, allowing an amount of the adhesive to be applied, to beincreased.

A concave-shaped area may be formed in the boundary portion between theexterior wall of the descender portion of the thrust member and theinterior wall at the base side edge of the hub side tubular wall suchthat a redundant component of the adhesive used for fixing the exteriorwall thereof and the interior wall thereof together is retained. In thiscase, an situation in which the adhesive has been applied can be readilyconfirmed, allowing variation in adhesive strength to be suppressed.

A protrusion extending in the outer diameter direction may be formed atthe base side edge of the descender portion of the thrust member. Inthis case, because the adhesive can be suppressed from entering thecapillary seal, allowing an amount of the adhesive to be applied, to beincreased.

The hub may fix the shaft such that one end of the shaft is directedtoward the sleeve, and the sleeve may store the shaft inside a tubularend surface. In this case, the tip of the shaft is protected if animpact is applied thereto, allowing an amount of scraped powder to begenerated, to be reduced.

The hub has a hole into which the shaft is press-fitted, and a stepportion may be formed on the shaft such that, among the shaft, theportion press-fitted into the hole has a smaller diameter than that ofanother portion. In this case, tilt of the shaft can be suppressed andthe adhesive can also be suppressed from entering the bearing portion,allowing an amount of the adhesive to be applied, to be increased.

When the diameter of the shaft is 2.5 mm or less, the force forextracting the shaft press-fitted into the hole of the hub, may be 600 Nor more. In this case, the disk drive device withstands the maximumimpact of 1300 G for a short time, allowing a possibility that a failuremay occur in practical use to be reduced.

The hub may have an inner circumferential wall of the annular portionand a protruded pedestal portion formed at a position spaced apart fromthe inner circumferential wall in the central direction of the hub, andfix the magnet with the pedestal portion and the inner circumferentialwall. In this case, the annular portion can be suppressed from beingthin because the pedestal portion is provided, allowing decrease in thestrength against the impact to be suppressed.

In the case where a recording disk is mounted on the hub, and when thecenter of gravity of the rotating body including the hub, the shaft andthe thrust member is located near a position where the hub and the shaftare fixed together, a distance between the center position of the statorcore in the direction from the base member toward the hub, and thecenter of gravity of the rotating body in the same direction, may be 1.8mm or less. In this case, the center position and the center of gravityare located closely to each other, allowing the impact resistance to beimproved.

Another embodiment of the present invention is also a disk drive device.The device comprises: a tubular sleeve that supports a shaft; a tubularhousing member that is arranged so as to surround the sleeve and makethe end of the sleeve protrude; a base member that holds the housingmember and fixes a stator core so as to surround the housing member; ahub that drives a recording disk by being rotated integrally with theshaft, with a magnet being fixed to an annular portion concentric withthe shaft so as to face the stator core fixed to the base member; and atubular thrust member that is rotated integrally with the hub. Thesleeve has a flange extending in the outer diameter direction at the hubside edge, and forms a first annular area between the flange and the hubside edge of the housing member; the base member forms a second annulararea on the outer circumference side of the housing member; the thrustmember has a ring portion that surrounds the sleeve and a descenderportion that surrounds the housing member, where the ring portion isfixed to the interior wall of a hub side tubular wall formed in the hub,and is rotated in the first area, and where the descender portion isjoined to the outer edge portion of the ring portion and fixed to theinterior wall of the hub side tubular wall, and is rotated in the secondarea; and a lubricant is filled between the housing member and thethrust member, and also between the flange of the sleeve and the hub.

According to the embodiment, because the thrust member has the descenderportion in addition to the ring portion, the fixing area with the hubcan be enlarged and the capacity of a capillary seal can be enlarged,allowing the impact resistance to be improved.

The thrust member may be formed by press working of a metallic material.In this case, generation of burr is reduced, allowing a possibility ofthe bun coming off due to an impact to be reduced.

In the ring portion of the thrust member, on at least one of the wallfacing the flange of the sleeve and the wall facing the hub side edge ofthe housing member, a thrust dynamic pressure groove for generating athrust dynamic pressure may be formed by press working. In this case,generation of the bun is reduced, allowing a possibility of the buncoming off due to an impact to be reduced.

The thrust member may be formed of a plastic material. In this case, thethrust member is formed by a metallic mold, allowing a possibility thatthe bun may be generated, to be reduced.

The interior wall of the descender portion of the thrust member may beformed such that the surface roughness thereof is Ry 1.6 or less. Inthis case, the gas-liquid boundary of the lubricant has a filletgeometry, allowing an amount of the lubricant to fall or be scattered tobe reduced even if an impact is applied.

A concave-shaped area may be formed in a place where the interior wallof the descender portion of the thrust member and the ring portion arejoined together. In this case, because the concave-shaped area isformed, the capacity of a capillary seal portion can be enlarged,allowing the capacity of the lubricant to be enlarged.

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments will now be described, by way of example only, withreference to the accompanying drawings which are meant to be exemplary,not limiting, and wherein like elements are numbered alike in severalFigures, in which:

FIG. 1 is a top view illustrating a structure of a disk drive deviceaccording to an embodiment of the present invention;

FIG. 2 is a cross-sectional view illustrating the structure of the diskdrive device in FIG. 1, taken along line A-A′ of FIG. 1;

FIG. 3 is a top view illustrating a communication passage of the diskdrive device in FIG. 2;

FIG. 4 is an enlarged cross-sectional view illustrating a thrust memberin FIG. 2;

FIG. 5 is an enlarged cross-sectional view illustrating the middleportion of the disk drive device in FIG. 2;

FIGS. 6A and 6B are partial cross-sectional views illustrating acapillary seal of the disk drive device in FIG. 2;

FIG. 7 is a partial cross-sectional view illustrating the center ofgravity of a rotating body and the center position of a stator core inthe disk drive device in FIG. 2; and

FIG. 8 is an enlarged cross-sectional view illustrating a disk drivedevice according to a variation of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

The invention will now be described by reference to the preferredembodiments. This does not intend to limit the scope of the presentinvention, but to exemplify the invention. An embodiment of the presentinvention is a disk drive device that is mounted in a hard disk driveand used for driving a magnetic recording disk, and a rotation speedthereof is, for example, 5400 rpm. Hereinafter, the same or equivalentconstituting elements and members illustrated in each drawing shall bedenoted by the same reference numerals, and the duplicative explanationswill be omitted appropriately. Dimensions of members illustrated in eachdrawing are appropriately enlarged or reduced for easier understanding.Part of members not important for describing the embodiment are omittedfrom each drawing.

FIG. 1 is a top view illustrating the structure of a disk drive device100 according to an embodiment of the present invention. The disk drivedevice 100 includes a hub 20, which is formed into a circular shape. Acentral hole 20 a is formed in the central portion of the hub 20, and ahub outward extension portion 20 d is formed in the outercircumferential portion thereof. Herein, the hub 20 is rotated aroundthe central hole 20 a. A disk 50 is formed into a donut shape. The innercircumferential portion of the disk 50 is fixed to the hub 20. As aresult, with the rotation of the hub 20, the disk 50 is also rotated.

FIG. 2 is a cross-sectional view illustrating the structure of the diskdrive device 100, taken along line A-A′ of FIG. 1. The disk drive device100 includes a fixed body S and a rotating body R. The fixed body Sincludes a base member 10, a stator core 12, a housing member 14 and asleeve 16; while the rotating body R includes the hub 20, a shaft 22 anda thrust member 26. The base member 10 includes a cylindrical portion 10a; the housing member 14 includes a groove 14 a, a bottom portion 14 b,a cylindrical portion 14 c and an upper end surface portion 14 d; thesleeve 16 includes an inner circumferential surface 16 a of thecylindrical portion, a flange portion 16 b and cylindrical portion 16 c;and coil 18 is wound around the stator core 12. The hub 20 includes thecentral hole 20 a, a first cylindrical portion 20 b, a secondcylindrical portion 20 c, the hub outward extension portion 20 d and apedestal portion 20 f; the shaft 22 includes a step portion 22 a, a tipportion 22 b and an outer circumferential surface 22 c; and the thrustmember 26 includes a descender portion 26 c and a ring portion 26 e. Inthe following descriptions, for convenience, the lower portion indicatedin the drawings is represented as the bottom, and the upper portion asthe top, as a whole.

The base member 10 has a central hole and the cylindrical portion 10 athat is provided so as to surround the central hole. The base member 10holds the housing member 14 with the central hole and fixes the statorcore 12 to the outer circumferential side of the cylindrical portion 10a that surrounds the housing member 14. A second annular area 42 isformed between the outer circumferential side of the housing member 14and the inner circumferential side of the cylindrical portion 10 a. Thesecond annular area 42 has a shape that surrounds the central hole ofthe base member 10. Herein, the base member 10 is formed by cutting ofan aluminum die cast material, or by press working of an aluminum sheetor a nickel-plated steel sheet.

The stator core 12 is fixed to the outer circumferential surface of thecylindrical portion 10 a. The stator core 12 is formed by performinginsulation coating such as electro-deposition coating and powder coatingon the surface thereof after a plurality of magnetic plates such asferrosilicon plates are laminated. The stator core 12 is ring-shaped soas to have a plurality of salient poles (not illustrated) protrudingoutwards, around each of which is wound the coil 18. When the disk drivedevice 100 is, for example, three-phase driven, the number of thesalient poles are designed to be nine. The wiring terminal of the coil18 is soldered on an FPC (Flexible Printed Circuits) arranged on thebottom surface of the base member 10.

The housing member 14 is fixed to the inner circumferential surface ofthe cylindrical portion 10 a by adhesion or press-fitting. The housingmember 14 has an approximate cup shape in which the cylindrical portion14 c surrounding the sleeve 16, the upper end surface portion 14 d thatis provided at the side end portion of the hub 20 and has a surface inthe axial direction, and the bottom portion 14 b that seals the endportion on the opposite side of the upper end surface portion 14 d amongthe cylindrical portion 14 c, are joined together. With such a shape,the housing member 14 is arranged so as to clog the lower end of thesleeve 16 and make the upper end thereof protrude. Herein, the bottomportion 14 b and the cylindrical portion 14 c may be integrally formed,or be formed by fixing them together as separate members. The housingmember 14 is formed of a plastic material such as polyetherimide,polyimide and polyamide as well as a copper alloy, a sintered alloy bypowder metallurgy, and stainless. When a plastic material is used in thehousing member 14, the member 14 is configured with a plastic materialincluding a carbon fiber such that the specific resistance of the member14 is 10⁶ (Ωm) or less in order to secure the static electricityremoval performance thereof.

Herein, the inner circumferential surface of the housing member 14 willbe described, referring to FIG. 3. FIG. 3 is a top view illustrating acommunication passage of the disk drive device 100. As illustrated, agroove 14 a extending in the axial direction is formed on the innercircumferential surface of the housing member 14. The groove 14 abecomes a communication hole through which both end surface sides of thehousing member 14 communicate with each other, when fitting the sleeve16 into the cylindrical portion 14 c. The communication hole becomes thecommunication passage I with the lubricant 28 being filled therein,which will be described in detail later. The cross-sectional shape ofthe groove 14 a is illustrated as being arc-shaped in FIG. 3, but notlimited thereto and may be any concave area recessed from the innercircumferential surface. Now, refer back to FIG. 2.

The sleeve 16 is fixed to the inner circumferential surface of thehousing member 14 by adhesion or press-fitting, and is fixed coaxiallywith the central hole of the base member 10. The sleeve 16 has, bystoring the shaft 22, a shape in which the annular cylindrical portion16 c that supports the shaft 22, and the flange portion 16 b extendingin the outer diameter direction at the side end portion of the hub 20 ofthe cylindrical portion 16 c, are joined together. The innercircumferential surface 16 a of the cylindrical portion is formed insidethe cylindrical portion 16 c, and the inner circumferential surface 16 aof the cylindrical portion surrounds the shaft 22. Herein, the flangeportion 16 b and the cylindrical portion 16 c may be integrally formed,or be formed by fixing them together as separate members. A firstannular area 40 is formed between the flange portion 16 b and thecylindrical portion 14 c. The sleeve 16 is formed of a plastic materialsuch as polyetherimide, polyimide and polyamide as well as a copperalloy, a sintered alloy by powder metallurgy, and stainless. When aplastic material is used in the sleeve 16, the sleeve 16 is configuredwith a plastic material including a carbon fiber such that the specificresistance of the sleeve 16 is 10⁶ (Ωm) or less in order to secure thestatic electricity removal performance thereof.

The hub 20 is configured to include the central hole 20 a provided inthe central portion thereof, the first cylindrical portion 20 b providedso as to surround the central hole 20 a, the second cylindrical portion20 c arranged outside the first cylindrical portion 20 b, and the huboutward extension portion 20 d extending outwards at the lower end ofthe second cylindrical portion 20 c. The hub 20 has an approximate cupshape. The thrust member 26 is fixed to the inner circumferentialsurface of the first cylindrical portion 20 b, and a ring-shaped magnet24 is fixed to the inner circumferential surface of the secondcylindrical portion 20 c. Herein, the ring-shaped magnet 24 is fixed tothe annular portion concentric with the shaft 22 so as to face thestator core 12 fixed to the base member 10. With such a structure, thehub 20 is rotated integrally with the shaft 22 to drive thenot-illustrated disk 50. The hub 20 is formed of a stainless materialhaving magnetism, and the not-illustrated disk 50 is mounted on the huboutward extension portion 20 d such that the central hole thereof isfitted into the outer circumferential surface of the second cylindricalportion 20 c.

The shaft 22 is fixed to the central hole 20 a. Herein, the upper endportion of the shaft 22 is provided with the step portion 22 a, and theshaft 22 is press-fitted into the central hole 20 a when assembling. Asa result, the hub 20 is restricted in the movement in the axialdirection by the step portion 22 a, and is integrated with the shaft 22at a predetermined right angle. The tip portion 22 b is stored in theinner circumference of the cylindrical portion 16 c. The shaft 22 isformed of a stainless material.

The thrust member 26 has the ring portion 26 e surrounding the sleeve 16and the descender portion 26 c surrounding the housing member 14.Herein, the ring portion 26 e is fixed to the interior wall of the firstcylindrical portion 20 b with an adhesive, and the descender portion 26c is joined to the outer edge portion of the ring portion 26 e and alsofixed to the interior wall of the first cylindrical portion 20 b with anadhesive. That is, the outer circumferential surface of the descenderportion 26 c is fixed to the inner circumferential surface of the firstcylindrical portion 20 b with an adhesive. With such a structure, thering portion 26 e surrounds the outer circumference of the cylindricalportion 16 c through a gap and is arranged on the lower surface of theflange portion 16 b thought a narrow gap. Further, the thrust member 26is rotated integrally with the hub, and at the time, the ring portion 26e is rotated in the first area 40 and the descender portion 26 c isrotated in the second area 42.

FIG. 4 is an enlarged cross-sectional view illustrating the thrustmember 26. The ring portion 26 e has a shape having a thrust uppersurface 26 a and a thrust lower surface 26 b, the shape being thin inthe axial direction. The descender portion 26 c extends in the axialdirection on the lower surface of the outer circumference side of thering portion 26 e. Further, the thrust member 26 joins the ring portion26 e and the descender portion 26 c together, and has a so-calledinverted L-shaped cross section in which the alphabetical capital letter“L” is inverted upside down. Herein, the length in the axial directionof the descender portion 26 c is larger than that in the axial directionof the ring portion 26 e. The inner circumferential surface 26 d of thedescender portion 26 c has a tapered shape, the radius of which isgradually smaller toward the side opposite to the ring portion 26 e, andcomposes a capillary seal, which will be described later. With such ashape, the thrust member 26 can be readily processed and becomesinexpensive. Further, when the thrust member 26 becomes small in sizeand thin, the thrust member 26 can be manufactured so as to have gooddimension accuracy. As a result, such a shape contributes to theminiaturization and light weight of the disk drive device 100. Now,refers back to FIG. 2.

The thrust member 26 prevents the rotating body R from coming off thefixed body S. When the rotating body R and the fixed body S relativelymove by an impact, the ring portion 26 e hit the lower surface of theflange portion 16 b. As a result, the thrust member 26 receives a stressin the direction in which the member 26 is detached from the firstcylindrical portion 20 b. If the joint distance between the descenderportion 26 c and the first cylindrical portion 20 b is small, the jointstrength becomes weak, causing a possibility that the joint therebetweenmay be destroyed by even a small impact to be high. That is, as thejoint distance between the descender portion 26 c and the firstcylindrical portion 20 b becomes longer, the joint therebetween becomesstronger against an impact.

On the other hand, as the ring portion 26 e becomes thicker, thecapillary seal portion becomes shorter, causing the capacity of thelubricant 28 that can be held in the capillary seal portion to be small.Therefore, there occurs a possibility that the lubricant 28 may be inshortage immediately after the lubricant 28 is scattered by an impact.Due to such shortage of the lubricant, the dynamic pressure groovebearing is deteriorated in its function, likely causing a malfunctionsuch as born-in. In order to deal with such a problem, the capillaryseal portion in the disk drive device 100 is designed to be long in theup-down direction by thinning the ring portion 26 e. As a result, anamount of the lubricant 28 that can be held becomes large, and the diskdrive device 100 is configured such that the lubricant 28 is hardly inshortage if a large amount thereof is scattered. That is, the distancein the axial direction of the thrust member 26 is designed to be largerelative to the descender portion 26 c and small relative to the ringportion 26 e.

There is a way in which the outer circumferential surface of thedescender portion 26 c is fixed to the inner circumferential surface ofthe first cylindrical portion 20 b by press-fitting; however, if thedescender portion 26 c receives a stress by the press-fitting,deformation occurs in the inner circumferential surface of the descenderportion 26 c, and therefore there is a fear that the function of thecapillary seal portion may be impaired due to the deformation. To dealwith the problem, the outer circumferential surface of the descenderportion 26 c is designed to have a smaller diameter than that of theinner circumferential surface of the first cylindrical portion 20 b suchthat both of them are fixed together by adhesion. As a result,deformation of the descender portion 26 c is prevented, allowing thefunction of the capillary seal to be fully demonstrated.

The ring-shaped magnet 24 is provided so as to be fixed to the innercircumference of the second cylindrical portion 20 c and to face theouter circumference of the stator core 12 through a narrow gap. Thering-shaped magnet 24 is formed of an Nd—Fe—B (Neodymium-Ferrum-Boron)material, the surface thereof being treated with electro-depositioncoating and splay coating, and the inner circumference thereof beingmagnetized in twelve poles.

Summarizing the descriptions up to now, the shaft 22 of the rotatingbody R is inserted in the inner circumferential surface 16 a of thecylindrical portion in the fixed body S; and the rotating body R isrotatably supported by the fixed body S through the dynamic pressuregroove, which is described later. The tip portion 22 b is set in size soas to face the bottom portion 14 b through a predetermined gap in thisstate. Further, the hub 20 structures a magnetic circuit with the statorcore 12 and the ring-shaped magnet 24, and each coil 18 thereof issequentially powered by the control from outside such that the rotatingbody R is rotatbly driven.

Subsequently, the dynamic pressure bearing in the structure of the diskdrive device 100 described up to now, will be described in detail. FIG.5 is an enlarged cross-sectional view illustrating the middle portion ofthe disk drive device 100. The dynamic pressure bearing in the radialdirection is configured to include the outer circumferential surface 22c, the inner circumferential surface 16 a of the cylindrical portion andthe lubricant 28 such as oil, etc., filled in the gap between the two.In the dynamic pressure bearing in the radial direction, a first radialdynamic pressure bearing RB1 and a second radial dynamic pressurebearing RB2 are arranged so as to be spaced apart from each other in theaxial direction, in which the former is arranged at a position moredistant from the hub 20 and the latter at a position nearer thereto. Thefirst radial dynamic pressure bearing RB1 and the second radial dynamicpressure bearing RB2 are arranged in the gap between the innercircumferential surface 16 a of the cylindrical portion and the outercircumferential surface 22 c such that a dynamic pressure in the radialdirection is generated to support the rotating body R. In the firstradial dynamic pressure bearing RB1 and the second radial dynamicpressure bearing RB2, at least one of the outer circumferential surface22 c and the inner circumferential surface 16 a of the cylindricalportion, which face each other, has a dynamic pressure groove forgenerating a dynamic pressure, formed thereon. The dynamic pressuregroove is formed into, for example, a herringborn-like shape.

When the rotating body R is rotated, the dynamic pressure groovegenerates a dynamic pressure such that the shaft 22 is supported by thedynamic pressure with a predetermined gap being created in the radialdirection relative to the sleeve 16. Herein, the width of the dynamicpressure groove in the axial direction in the first radial dynamicpressure bearing RB1, is designed to be narrower than that in the axialdirection in the second radial dynamic pressure bearing RB2. Thereby,dynamic pressures corresponding to lateral pressures having a strengthdifferent from each other in the axial direction of the shaft 22, aregenerated in the first radial dynamic pressure bearing RB1 and thesecond radial dynamic pressure bearing RB2, allowing optimal balancebetween high shaft stiffness and low shaft loss to be acquired.

On the other hand, the dynamic pressure bearing in the thrust directionincludes at least one of a first thrust dynamic pressure bearing SB1, asecond thrust dynamic pressure bearing SB2 and a third thrust dynamicpressure bearing SB3. Herein, the first thrust dynamic pressure bearingSB1 is formed by the lubricant 28 filled in the gap in the axialdirection between the thrust upper surface 26 a of the thrust member 26fixed to the hub 20, and the lower surface of the flange portion 16 b.The second thrust dynamic pressure bearing SB2 is formed by thelubricant 28 filled in the gap in the axial direction between the thrustlower surface 26 b and the upper end surface portion 14 d. The thirdthrust dynamic pressure bearing SB3 is formed by the lubricant 28 filledin the gap in the axial direction between the lower surface 20 e and theupper surface of the flange portion 16 b. In the following description,at least one of the first thrust dynamic pressure bearing SB1 to thethird thrust dynamic pressure bearing SB3 is collectively referred to asa thrust dynamic pressure bearing SB.

On one of the surfaces facing each other of each of these gaps in theaxial direction, is formed the thrust dynamic pressure groove (notillustrated) for generating a dynamic pressure. The thrust dynamicpressure groove is formed into, for example, a spiral-like orherringborn-like shape, and generates a pump-in dynamic pressure. Withthe rotation of the rotating body R, the thrust dynamic pressure bearingSB generates a pump-in dynamic pressure by the dynamic pressure, andexerts a force in the axial direction on the rotating body R by thepressure thus generated. The lubricants 28 filled in the gaps in thefirst radial dynamic pressure bearing RB1, the second radial dynamicpressure bearing RB2 and the thrust dynamic pressure bearing SB, areused in common with each other, and are prevented from leaking outwardsby being sealed with the capillary seal portion, which will be describedin the following description.

The capillary seal portion TS is structured with the outercircumferential surface of a member composing the fixed body S such asthe sleeve 16 or the housing member 14 (hereinafter, referred to as“fixed body outer circumferential surface”) and the innercircumferential surface 26 d of the thrust member 26. The fixed bodyouter circumferential surface has an inclined surface, the diameter ofwhich becomes gradually smaller when proceeding from the upper surfaceside to the lower surface side. The inclined surface is formed so as tohave an inclined angle bis relative to the rotational center line of theshaft 22. On the other hand, the inner circumferential surface 26 dfacing thereto also has an inclined surface, the diameter of whichbecomes gradually smaller when proceeding from the upper surface side tothe lower surface side. The inclined surface is formed so as to have aninclined angle θh relative to the rotational center line of the shaft22, the inclined angle φh being set to be greater than 0° and smallerthan the inclined angle θis. That is, the relationship: 0<θh<θis holds.

With such a structure, the fixed body outer circumferential surface andthe inner circumferential surface 26 d form the capillary seal portionTS, the gap of which becomes gradually wider when proceeding from theupper surface side to the lower surface side. Herein, because an amountof the lubricant 28 to be filled in the gap is set such that theboundary surface (fluid level) between the lubricant 28 and ambient airis located in the middle of the capillary seal portion TS, the lubricant28 is sealed with the capillary seal portion TS by capillarity. As aresult, the lubricant 28 is prevented from leaking outwards. That is,the lubricant 28 is filled between the housing member 14 and the thrustmember 26 and also between the flange portion 16 b and the hub 20.

As stated above, the capillary seal portion TS is designed such that theinner circumferential surface 26 d thereof, an outside inclined surfacethereof, has a diameter that becomes gradually smaller when proceedingfrom the upper surface side to the lower surface side. Thereby, with therotation of the rotating body R, a centrifugal force in the directionwhere the lubricant 28 is moved toward the inside of the portion inwhich the lubricant is filled, is exerted on the lubricant 28,preventing, more surely, the lubricant 28 from leaking outwards. Thecommunication passage I is secured by the groove 14 a formed in thedirection axially along the inner circumferential surface of the housingmember 14. Because both sides of the first radial dynamic pressurebearing RB1 and the second radial dynamic pressure bearing RB2 arecommunicated with each other by the communication passage I, the wholepressure balance can be maintained at a good level even if an individualpressure balance of the radial dynamic pressure bearing is notmaintained. Further, even if the balance among the dynamic pressures ofthe first radial dynamic pressure bearing RB1, the second radial dynamicpressure bearing RB2 and the thrust dynamic pressure bearing SB, is notmaintained by a disturbance such as an force from outside exerted on theshaft 22 or the rotating body R, the pressures are instantly averaged tomaintain the pressure balance. As a result, a floating amount of therotating body R is stabilized relative to the fixed body S, allowing thedisk drive device 100 with high-reliability to be acquired.

When assembling the disk drive device 100 according to the embodiment,for example, the sleeve 16 and the housing member 14 are integrated byadhesion or the like such that the thrust member 26 is sandwiched bythem. Subsequently, when inserting the shaft 22 fixed to the hub 20 intothe sleeve 16 thus assembled, the thrust member 26 may be fixed to thehub 20 by adhesion or press-fitting.

Subsequently, the structure of the disk drive device 100 will bedescribed further in detail. Hereinafter, each item will be described as(1) to (13), but these items may be used in an arbitrary combination.

(1) When performing cutting on, for example, a metallic material to formthe aforementioned thrust member 26, there is a problem that the cuttingneeds many efforts and a lot of fine burr remains on the surface or inthe corner section thereof. The fine bun, after coming off due to animpact, etc., enters narrow gaps to deteriorate the rotational accuracy.Further, the fine burr entering narrow gaps promotes wearing of thebaring unit, etc., causing a malfunction such as burn-in in a shorttime. To solve such problems, the thrust member 26 is formed by pressworking of a metallic material. As a result, the efforts for the workingcan be trimmed, and generation of the bun causing a problem can bereduced. For example, a donut-shaped base material is cut off from astainless sheet such as SUS 304 having a thickness of 0.6 mm, and thenthe outer circumference thereof is pressed by press working; thereby,the thrust member 26 having an approximate cup shape, at the center ofwhich a hole is opened, is formed. In this case, the thickness dimensionof the ring portion 26 e can be readily and accurately measured with aheight gauge, etc., by making the upper surface of the descender portion26 c slightly lower than that of the ring portion 26 e. If necessary,grinding with a barrel, etc., may be appropriately performed.

(2) The thrust dynamic pressure groove is also formed by rolling orcutting, but there is a problem that theses workings need many effortsand fine bun remains on the surface or in the corner section thereof.The fine burr comes off due to an impact, etc., and enters narrow gapsto deteriorate the rotational accuracy. Further, the fine bun enteringnarrow gaps promotes wearing of the baring unit, etc., causing amalfunction such as burn-in in a short time. To deal with such problems,in the ring portion 26 e, thrust dynamic pressure grooves for generatinga thrust dynamic pressure are formed by press working on the wall facingthe flange portion 16 b and the wall facing the upper end surfaceportion 14 d. As a result, the efforts for the working can be trimmed,and generation of the burr causing a problem can be reduced.

(3) The thrust member 26 may be formed of a plastic material. As aresult, the member can be accurately manufactured in a short time byusing a metallic mold. Herein, the plastic material is not particularlylimited, but as materials having a similar effect, polyetherimide,polyamide and polyimide and the like are more preferred in terms ofcharacteristics such as accuracy and mechanical strength.

(4) In the case where the outer circumferential surface of the descenderportion 26 c and the inner circumferential surface of the firstcylindrical portion 20 b are fixed together with an adhesive, whenintending the adhesive strength is strong, it is needed that an amountof the adhesive to be applied is made large. However, there is a problemthat the function of the capillary seal is deteriorated with theadhesive that leaks out from the adhesion surface entering the capillaryseal portion TS beyond the tip portion of the descender portion 26 c. Todeal with the problem, the base side edge of the descender portion 26 cof the thrust member 26 is formed so as to more protrude than the baseside edge of the first cylindrical portion 20 b. Describing it in moredetail, the tip portion of the descender portion 26 c of the thrustmember 26 is formed so as to extend more downwards than the tip portionof the first cylindrical portion 20 b of the hub 20. As a result, it issuppressed that the adhesive leaking out from the adhesion surfacebetween the two, enters the capillary seal portion TS beyond the tip ofthe descender portion 26 c. Thereby, a sufficient amount of adhesive canbe applied, allowing required adhesive strength to be secured.

(5) When the outer circumferential surface of the descender portion 26 cand the inner circumferential surface of the first cylindrical portion20 b are fixed together with an adhesive, an amount of the adhesive tobe applied is individually varied, causing a variation in the adhesivestrength. Because an individual situation of applying the adhesivecannot be easily observed, there is a problem that a product having lowadhesive strength due to an insufficient amount of the adhesive to beapplied, is put on the market without being found in the manufacturingline. To deal with the problem, in the boundary portion between theexterior wall of the descender portion 26 c and the interior wall at thebase side edge of the first cylindrical portion 20 b, a concave-shapedarea is formed such that a redundant component of the adhesive used forfixing the exterior wall thereof and the interior wall thereof together,is retained. That is, by providing the concave area in the boundaryportion between the descender portion 26 c and the first cylindricalportion 20 b and by filling the lubricant between the two, a state wherethe lubricant is sufficiently filled in the concave area can be visuallyand easily observed. Accordingly, if the lubricant is not sufficientlyapplied, the lubricant can be additionally applied; and thereby there isan effect that a variation in the adhesive strength can be suppressedand the impact resistance can be improved.

(6) As stated above, when intending the adhesive strength to be strongin the case where the outer circumferential surface of the descenderportion 26 c and the inner circumferential surface of the firstcylindrical portion 20 b are fixed together with an adhesive, an amountof the adhesive to be applied is needed to be large. However, there is aproblem that the function of the capillary seal is deteriorated with theadhesive that leaks out from the adhesion surface between the twoentering the capillary seal portion TS beyond the tip of the descenderportion 26 c. To deal with this, a protrusion extending in the outerdiameter direction is formed at the base side edge of the descenderportion 26 c. That is, a convex area extending outwards is provided inthe tip of the descender portion 26 c. As a result, the lubricantleaking in this portion is blocked, and hence the lubricant can beprevented from entering the capillary seal portion TS. Thereby, asufficient amount of the adhesive can be applied such that the requiredadhesive strength is secured.

(7) The lubricant 28 is held by a surface tension and a centrifugalforce in the capillary seal portion TS. FIGS. 6A and 6B are partialcross-sectional views illustrating the capillary seal of the disk drivedevice 100. FIG. 6A illustrates a structure of a disk drive device to becompared with the disk drive device 100 according to the presentembodiment. If the surface roughness of the inner circumferentialsurface 126 d of a descender portion 126 c of a thrust member 126 ispoor, a contact angle on the surface becomes large. As a result, thegas-liquid boundary 128 a of a lubricant has a fillet geometry asillustrated in FIG. 6A. In the case of such a geometry, if the lubricantin a capillary seal portion TS becomes insufficient by falling andscattering, the lubricant is in shortage in a short time, thereby thereis a problem that a failure such as burn-in, etc., may occur. To dealwith this, the inner circumferential surface 26 d is formed such thatthe surface roughness thereof is Ry 1.6 or less. As a result, thecontact angle becomes small, allowing the gas-liquid boundary 28 a tohave a fillet geometry as illustrated in FIG. 6B. Thereby, there is aneffect that an amount of the lubricant 28 lost by falling and scatteringis reduced to the minimum level if an impact acceleration is applied tothe lubricant 28. Alternatively, the required surface roughness thereofcan be acquired by enhancing the surface roughness of a metallic moldduring press working and then by finishing the surface multiple times aswell as performing polishing on the tip of the descender portion 26c. Itis more preferable that the surface roughness thereof is made Ry 0.8 orless, allowing the impact resistance to be more improved.

(8) If the capacity of the capillary seal portion TS is small, there isa problem that, when the lubricant 28 is scattered by an impact, thelubricant 28 is easily in shortage, causing a failure such as burn-in,etc. To deal with this, a concave-shaped area is formed in a place wherethe inner circumferential surface 26 d of the descender portion 26 c andthe ring portion 26 e are joined together. As a result, there is aneffect that the space of the concave area becomes part of the capillaryseal portion TS to increase the capacity thereof, and hence thelubricant 28 is hardly in shortage if the lubricant 28 is scattered dueto an impact, allowing the impact resistance to be improved.

(9) With the demand for thinning the disk drive device 100, the housingmember 14 is also requested to be thin. However, when the housing member14 is thin, the stiffness thereof is deteriorated, and hence the housingmember 14 undergoes elastic deformation due to an impact from outsidesuch that the member 14 is in contact with the tip portion 22 b. In thiscase, there is a problem that a contact between the rotating body andthe fixed body generates scraped powder and the scraped powder enters anarrow gap, causing wearing to be accelerated or the bearing to be in amalfunction such as burn-in, etc. To deal with this, the shaft 22 may befixed to the hub 20 such that one end of the shaft 22 is directed towardthe sleeve 16, and the sleeve 16 stores the shaft 22 inside the tubularend surface. That is, the lower end of the sleeve 16 can be configuredto protrude from the tip portion 22 b. As a result, if the housingmember 14 undergoes elastic deformation, it is blocked by the lower endof the sleeve 16, preventing the contact thereof with the tip portion 22b. With this structure, such a problem can be suppressed withoutgenerating the scraped powder due to an impact.

(10) The shaft 22 is fixed to the central hole of the hub 20 bypress-fitting or adhesion. However, in order to thin the disk drivedevice 100, the portion of the hub 20 to be fitted into the shaft 22 issmall in length, and hence it becomes difficult to secure sufficientstrength against an impact. When a large amount of the adhesive isapplied to increase the strength, the adhesive leaks out to enter thebearing unit, causing a problem that a malfunction may occur. Further,because the disk 50 is mounted on the outer circumference of the hub 20,a large stress is, when an impact is applied, exerted on the fitting-inportion between the hub 20 and the shaft 22, with the mass of the diskbeing added thereto, casing a failure such as deformation, etc., tolikely occur. For example, if the hub 20 deforms so as to lean towardthe shaft 22 due to an impact, the lower surface of the hub 20 and theupper surface of the flange portion 16 b are in contact with each other,causing a problem that a malfunction may occur. To deal with suchproblems, the hub 20 has the central hole 20 a into which the shaft 22is press-fitted, and the step portion 22 a is formed on the shaft suchthat, among the shaft, the portion press-fitted into the hole has asmaller diameter than that of another portion. As a result, because thelean of the hub 20 is suppressed and the strength is increased, and alsobecause the adhesive is, even if the adhesive leaks out, prevented fromentering the bearing unit, a larger amount of the adhesive can beapplied, allowing the impact resistance thereof to be greatly improved.For example, the shaft 22 has a diameter of 2.5 mm and the step portion22 a has that of 2.1 mm, and therefore a seat portion having a depth of0.2 mm on either side thereof, is provided.

(11) Until now, a shaft having a diameter of 3.0 mm is used in diskdrive devices even for mobile applications. In the case, the force forextracting the shaft from the hub is designed to be approximately 300 N.However, in order to reduce a current, the disk drive device has to beconfigured to have a thin shaft having a diameter of 2.5 mm or less. Onthe other hand, in order not to cause a failure while the disk drivedevice is actually being used, the device preferably has the impactresistance of 1300 G or more as the maximum impact for a short time, forexample 1 ms. To solve such a problem, the force for extracting theshaft 22 fitted into the central hole 20 a of the hub 20 is designed tobe 600 N or more, when the shaft 22 has a diameter of 2.5 mm or less.With such a structure, the disk drive device can withstand an impact of1300 G or more as the maximum impact for a short time, for example, 1ms.

Hereinafter, a specific example will be described. The shaft 22 made ofstainless has a diameter of 2.5 mm and the step portion 22 a thereofhaving a smaller diameter has that of 2.1 mm; and the surface roughnessin the step portion is Ra 0.15 or less. In such a structure, in order tofurther increase the strength, a recess (concave area) in the radialdirection at the base of the step portion 22 a is eliminated such that arounded portion having Ra 0.07 or less is provided. On the other hand,the central hole 20 a of the hub 20 made of stainless is designed tohave a diameter of 2.1 mm such that the shaft 22 is fixed to the hub 20by light press-fitting and adhesion combined together, the lightpress-fitting being performed with a press-fitting interference being 15μm to 20 μm to adjust dimension tolerances. The length in the axialdirection of the fitting-in portion between the shaft 22 and the centralhole 20 a is designed to be 1.44 mm. Assembly is performed in a way thatthe step portion 22 a of the shaft 22, having a smaller diameter, isapplied with the adhesive, and then slowly press-fitted into the centralhole 20 a; thereby the shaft 22 being smoothly assembled at apredetermined position. The shaft 22 can be smoothly press-fitted intothe hole, because the surface roughness of the shaft 22 is as fine as Ra0.15 or less and the adhesive applied thereto functions as a lubricantat the press-fitting. With such a structure, the force for extractingthe shaft 22 from the hub 20 is 600 N or more, thereby the disk drivedevice 100 that can withstand an impact of 1300 G or more as the maximumimpact for a short time, for example, 1 ms, can be structured. Inaddition, components and manufacturing steps for the device 100 can bereadily managed by checking the force for extracting the shaft 22, withthe sample inspection in manufacturing the devices.

(12) In a disk drive device, when the inner surface of the hub isprocessed by cutting with a byte, a place where the cutting is notperformed is generated inside the corner section of the hub, the placehaving a width corresponding to the radius Rb of the tip of the byte.The radius Rb of the tip of the byte has at smallest a limit ofapproximately 0.2 mm in practical use, but never reduced to 0.Conversely, when Rb is made small, an area to be cut in one rotation ofthe byte is decreased, and hence the period necessary for cutting thewhole of the hub is inversely increased and wearing of the byte isintensified. When there is a place where the cutting is not performed,the place having a width corresponding to the radius Rb of the tip ofthe byte, at the corner section of the inner circumferential surface,the ring-shaped magnet is, when fixing the magnet to such a place,spaced apart therefrom because of interference with the outercircumferential corner section of the magnet and such the place. Inorder to prevent this, a concave area is generally provided in theradial direction at the corner section of the second cylindricalportion; however, the concave area deceases the strength of the secondcylindrical portion.

Further, because a disk having a large mass is mounted on the outercircumference of the hub, a large stress is, when a large impactacceleration, for example, 1300 G, is applied, exerted in the radialdirection, with the mass of the disk being added to; and therefore thehub is likely to deform. The deformation of such a place entailsdeformation of the inner circumference of the ring-shaped magnet.Thereby, the coaxial degree with the outer circumference of the statorcore facing through a narrow gap, is deteriorated such that a rotationalfluctuation occurs, causing a malfunction in the disk drive device. Atworst, there is a problem that the inner circumference of thering-shaped magnet is partially in contact with the outer circumferenceof the stator core, causing a serious malfunction.

To deal with the problem, the hub 20 has the inner circumferential wallof the second cylindrical portion 20 c, and the protruded pedestalportion 20 f formed at a position spaced apart from the innercircumferential wall in the central direction of the hub 20. Thering-shaped magnet 24 is fixed with the pedestal portion 20 f and theinner circumferential wall of the second cylindrical portion 20 c. Byproviding the pedestal portion 20 f in a portion where the hub 20 to becut by a byte and the outer circumferential corner section of the uppersurface of the ring-shaped magnet 24 are in contact with each other, theimpact resistance thereof can be improved. Because the thickness in theup-down direction of the hub 20 is larger than that in thecircumferential direction of the second cylindrical portion 20 c, thestrength thereof is less decreased when the pedestal portion 20 f isprovided, and deformation thereof hardly occurs. Further, because thedeformation, even if occurs, occurs in the axial direction, theinfluence by the deformation on the gap between the ring-shaped magnet24 and the stator core 12 is small. Therefore, even if a large impactacceleration is applied, a possibility that a malfunction may occur inthe disk drive device 100 is small.

(13) In a disk drive device until now, when a disk is mounted on theouter circumference of the hub, the hub is to support a large mass. Ifan impact acceleration is applied in such a state, a large stress isexerted on the hub with the large mass being added to. In a state wherea disk is mounted, when the gravity of center of the rotating body suchas the ring-shaped magnet, which is rotated integrally with the hub, islocated on the center line of rotation and near the fitting-in portionbetween the hub and the shaft, deformation occurs such that the hub andthe disk tilt, with the fitting-in portion between the hub and the shaftbeing a fulcrum point, if an impact acceleration is applied in the axialdirection. If such deformation occurs even slightly, the gap between theinner circumference of the ring-shaped magnet and the outercircumference of the stator core, becomes non-uniform. Suchnon-uniformity causes a variation in rotation, and at worst, scrapedpowder is generated by a contact between the two. Also, there is aproblem that the scraped powder travels in the gap, becoming an obstaclefor rotation.

To solve such a problem, a way can be considered in which the gapbetween the inner circumference of the ring-shaped magnet and the outercircumference of the stator core is made large; however, the wayincreases a magnetic resistance, leading to decrease in the magneticflux. Thereby, there is a harmful effect that the torque is decreasedand increase in the leaking magnetic flux adversely affects the magnetichead. Also, another way can be considered in which, by making thediameter of the outer circumference of the hub small, the gap betweenthe inner circumference of the ring-shaped magnet and the outercircumference of the stator core is less affected by the tilt of therotating body; however, the way decreases the torque, leading toincrease in a current. Therefore, these ways cannot be adopted.

To deal with the problem, when the center of gravity G of the rotatingbody R is, in the case where the disk 50 is mounted on the hub 20,located near the place where the hub 20 and the shaft 22 are fixedtogether, the disk drive device 100 is structured as follows: thedistance between the center position of the stator core 12 in thedirection toward the hub 20 from the base member 10, and the center ofgravity G of the rotating body R in the same direction, is designed tobe 1.8 mm or less. With such a structure, the impact resistance can beimproved. In known techniques, the distance in the axial directionbetween the center position in the axial direction of the stator coreand the center of gravity of the rotating body is, for example, 2.0 mmor more, causing the impact resistance to be insufficient.

FIG. 7 is a partial cross-sectional view illustrating the center ofgravity of the rotating body R and the center position of the statorcore in the disk drive device 100. In FIG. 7, G indicates a position ofthe center of gravity of the rotating body R including the disk 50,which is located on the center line of rotation and near the fitting-inportion between the hub 20 and the shaft 22. For example, the diameterof the outer circumference of the hub 20 is designed to be 15 to 25 mm,and the gap between the inner circumference of the ring-shaped magnet 24and the outer circumference of the stator core 12 to be 0.1 to 0.3 mm.Further, by making the thickness of the portion immediately below thecoil 18 of the base member 10 thick, the position of the stator core 12is moved upwards, and the center position C in the axial direction ofthe stator core 12 is designed to be spaced 1.8 mm or less apart in theaxial direction from the center of gravity of the rotating body R. InFIG. 7, the distance in the axial direction is indicated as D.

As a result, if an impact of 1300 G is applied, a possibility that theinner circumference of the ring-shaped magnet 24 and the outercircumference of the stator core 12 may be in contact with each other isreduced, allowing the impact resistance to be improved. When thedistance in the axial direction is set so as to be small, the basemember 10 can be made thicker with it, allowing the stiffness thereof tobe enhanced and the impact resistance to be improved. More preferably,the impact resistance can be further improved by designing such adistance D in the axial direction to be 1.6 mm or less. However, withthe position in the axial direction of the stator core 12 being higher,the coil 18 wound around the stator core 12 becomes in contact with thelower surface of the hub 20, and therefore the lower limit of thedistance D in the axial direction is set to 1.2 mm. Further, by makingthe thickness of the portion immediately below the coil 18 of the basemember 10, 150% or more relative to that of the portion immediately onthe coil 18 of the hub 20, the stiffness of the base member 10 isenhanced and the mass of the rotation body is reduced, allowing theimpact resistance to be improved. In a specific example, the thicknessof the portion immediately below the coil 18 of the base member 10 ismade 1.5 mm, and that of the portion immediately on the coil 18 of thehub 20 is made 1.0 mm. It is noted that the thickness dimensions aremeasured with a hole or concavities and convexities being excluded. Ifthe thickness of the portion immediately on the coil 18 of the hub 20 ismade 0.5 mm or less, the stiffness of the hub 20 is often insufficient,and therefore the upper limit is set to 400%.

It has been described that the aforementioned thrust dynamic pressurebearing SB is structured with the gap in the axial direction of any oneof the first thrust dynamic pressure bearing SB1, the second thrustdynamic pressure bearing SB2 and the third thrust dynamic pressurebearing SB3. However, it is possible that the thrust dynamic pressurebearing SB is structured with two or three of the gaps in the axialdirection where dynamic pressures are generated, so that the actionsthereof are complementary to each other. Such structure does not departfrom the spirit and scope of the present invention.

Subsequently, a variation thereof will be described. The variationrelates to the same disk drive device 100 as in the present embodiment.In the embodiment, the thrust member 26 includes the ring portion 26 eand the descender portion 26 c. On the other hand, in the variation, thethrust member includes only the descender portion. Such a descenderportion may be considered to be a ring portion, but herein will bedescribed as a descender portion. FIG. 8 is an enlarged cross-sectionalview illustrating a disk drive device 100 according to the variation ofthe present invention. In FIG. 8, components common with those in FIG.2, etc., are denoted with the same reference numerals and descriptionsthereof will be omitted. In each of the first radial dynamic pressurebearing RB1 and the second radial dynamic pressure bearing RB2, forexample, a heringborn-like dynamic pressure groove for generating adynamic pressure is formed in at least one of the outer circumferentialsurface 22 c and the inner circumferential surface 16 a of thecylindrical portion in a gap between the two, in the same way as untilnow. On the other hand, in the thrust dynamic pressure bearing SB, forexample, a spiral-shaped thrust dynamic pressure groove (notillustrated) for generating a dynamic pressure is formed on one of thelower surface 20 e and the upper surface of the flange portion 16 b,which face each other, in a gap in the axial direction between the two.

The thrust member 30 includes the upper end portion 30 a, the descenderportion 30 b, the outer circumferential surface 30 c and the innercircumferential surface 30 d. That is, the thrust member 30 does notinclude the ring portion 26 e, but has an approximate ring shape such asthe descender portion 30 b corresponding to the descender portion 26 c.The upper end portion 30 a faces the lower surface of the flange portion16 b of the sleeve 16 so as to create a narrow gap, and performs afunction of preventing the thrust member from coming off. The outercircumferential surface 30 c of the descender portion 30 b is fixed tothe inner circumferential surface of the first cylindrical portion 20 bof the hub 20. When structuring the two by fixing them with an adhesive,a concave area as illustrated in FIG. 8 may be provided on the innercircumferential surface of the first cylindrical portion 20 b of the hub20, as a place where the adhesive is retained, thereby adhesive strengthbeing improved and leaking out of the adhesive being prevented.

The capillary seal portion TS is structured with the outercircumferential surface of a member composing the fixed body S such asthe sleeve 16 or the housing member 14 (hereinafter, referred to as“fixed body outer circumferential surface”) and the innercircumferential surface 30d of the descender portion 30 b of the thrustmember 30. The dimension in the radial direction (dimension in thevertical direction of FIG. 8) of the thrust member 30 is designed to beas short as 0.3 to 0.5 mm such that the space in the radial direction isnot occupied uselessly, allowing the dimensions of the bearing portionand stator core 12 portion to be large. On the other hand, by making thedimension in the axial direction (dimension in the vertical direction ofFIG. 8) of the thrust member 30 as large as 1.5 to 3.0 mm, the capacityof the capillary seal portion TS on the inner circumferential surface isenlarged, and the fixing strength to the inner circumferential surfaceof the first cylindrical portion 20 b is enhanced.

The not-illustrated communication passage I is secured by the groove 14a formed in the direction axially along the inner circumferentialsurface of the housing member 14, and by a groove formed, among theupper surface of the housing member 14, in a portion where the uppersurface thereof is in contact with the upper surface of the flangeportion 16 b. Both sides of the first radial dynamic pressure bearingRB1 and the second radial dynamic pressure bearing RB2 are communicatedwith each other by the communication passage I, the whole pressurebalance can be maintained at a good level, even if an individualpressure balance of the radial dynamic pressure bearing is notmaintained.

Also, with respect to the thrust member 30, the following items may bearbitrarily adopted in the same way as the embodiment: the member 30 isformed by press working of a metallic material; the member 30 is formedof a plastic material; the tip of the descender portion 30 b extendsmore downwards than that of the first cylindrical portion 20 b; aconcave area is provided at the boundary portion between the outercircumferential surface of the descender portion 30 b and the tip of thefirst cylindrical portion 20 b such that an adhesive is filled therein;the tip of the descender portion 30 b is provided with a convex areaextending outwards; and the surface roughness of the innercircumferential surface 30 d is Ry 1.6 or less. Needless to say, it isclear that operations and effects by the aforementioned items are thesame as those of the embodiment.

The following items may be arbitrarily adopted in the same way as theembodiment: the lower end of the sleeve 16 is made protrude from thelower end of the shaft 22; among the shaft 22, the diameter of a portionthereof where the shaft 22 is fitted into the central hole 20 a, is madesmaller than that of another portion such that the step portion 22 a isprovided; in the case where the diameter of the shaft 22 is 2.5 mm orless, the force for extracting the shaft 22 from the central hole 20 ais to be 600 N or more; the pedestal portion 20 f is provided in the hub20 that is to be processed by cutting with a byte, so that the pedestalportion 20 f and the ring-shaped magnet 24 are configured to be incontact with each other; the distance in the axial direction between thecenter position in the axial direction of the stator core 12 and thecenter of gravity of the rotating body R, is to be 1.8 mm or less; andthe thickness of the portion immediately below the coil 18 of the basemember 10 is to be 150% or more relative to that of the portionimmediately on the coil 18 of the hub 20. Needless to say, it is clearthat operations and effects by the aforementioned items are the same asthose of the embodiment.

According to the embodiment of the present invention, the thrust memberhas the descender portion in addition to the ring portion, and hence thefixing area with the hub can be enlarged. Further, because the fixingarea with the hub is enlarged, the impact resistance can be improved.Further, because the thrust member has the descender portion in additionto the ring portion, the capacity of the capillary seal can be enlarged.Further, because the capacity of the capillary seal is enlarged, anamount of the lubricant can be enlarged. Because the amount thereof isenlarged, the impact resistance can be improved. Further, because thethrust member is fixed to the hub with an adhesive, deformation of thedescender portion can be suppressed. Further, because the deformationthereof is suppressed, the function of the capillary seal can besecured. Further, the function of the capillary seal is secured, theimpact resistance can be improved. Further, a disk drive device in whicha failure or a malfunction never occurs in a short time even if a largeimpact is applied thereto, can be provided. Further, such a disk drivedevice can be used in a wide range of applications such as mobiledevices to which larger impacts are applied. Further, a disk drivedevice that is smaller in size, thinner, and lighter in weight, incomparison with another device having the same impact resistance as theaforementioned one, can be readily realized.

The present invention should not be limited to each of theaforementioned embodiments, and various modifications such as designmodifications, can be made with respect to the above embodiments basedon the knowledge of those skilled in the art. The structure illustratedin each drawing is intended to exemplify an example, and the structurecan be appropriately modified to a structure having a similar function,which can provide similar effects.

In the embodiment of the present invention, the thrust member 26 isfixed to the hub 20 with an adhesive. However, without limiting thereto,the thrust member 26 may not be fixed to the hub 20 with an adhesive,but fixed thereto with another measure. According to the presentvariation, the degree of freedom in fixing them together can beimproved.

In the embodiment of the present invention, the sleeve 16 and thehousing member 14 are structured as separate members. However, withoutlimiting thereto, for example, the sleeve 16 and the housing member 14may be formed integrally. In the case, the communication passage I maybe a hole penetrating from the lower surface of the sleeve 16 throughthe upper surface of the flange portion 16 b. According to the presentvariation, the degree of freedom in designing the disk drive device 100can be improved.

What is claimed is:
 1. A disk drive device comprising: a hub on which arecording disk is to be mounted; a shaft that is rotated integrally withthe hub; a supporting member that surrounds the shaft and that has aflange radially extending outward at the hub side edge; a base memberthat supports the supporting member; and a cylindrical thrust memberthat is rotated integrally with the hub, wherein a diameter of the shaftis 2.5 mm or less, wherein the hub is formed of a stainless materialhaving magnetism and has an annular portion, wherein a magnet is fixedto an inner circumferential surface of the annular portion, wherein thehub has a step portion on an inner portion of the hub, wherein a topportion of the thrust member is partially affixed to the step portion ofthe hub in the axial direction, and wherein a part of the top portion ofthe thrust member not partially affixed axially faces at least part ofthe flange.
 2. The disk drive device according to claim 1, wherein thesupporting member has an inner member that surrounds the shaft and anouter member that surrounds the inner member, and wherein the outermember is in a cup-like shape and formed from a stainless material, acopper alloy, or a sintered alloy by powder metallurgy.
 3. The diskdrive device according to claim 1, wherein the hub has a descendingportion that axially extends towards the base member and that annularlysurrounds part of the supporting member within the inner portion of thehub, wherein the thrust member is affixed with an adhesive to the innerportion of the hub along the descending portion of the hub, so as toallow the thrust member to rotate with the shaft, and wherein a baseside edge of the thrust member is formed so as to protrude beyond thedescending portion of the hub in the axial direction.
 4. The disk drivedevice according to claim 1, wherein the base member is formed of analuminum sheet or a steel plate.
 5. The disk drive device according toclaim 1, wherein the hub has a protruded pedestal portion formed at aposition spaced apart from the annular portion in the central directionof the hub, and fixes the magnet with the pedestal portion and the innercircumferential surface of the annular portion.
 6. The disk drive deviceaccording to claim 1, wherein the base member has an ascending portionthat axially extends towards the hub and that annularly surrounds partof the supporting member within the inner portion of the hub, whereinthe supporting member and the ascending portion form an annular area,and wherein the base side edge of the thrust member is rotated in theannular area.
 7. A disk drive device comprising: a hub on which arecording disk is to be mounted; a shaft that is rotated integrally withthe hub; a supporting member that surrounds the shaft and that has aflange radially extending outward at the hub side edge; a base memberthat supports the supporting member; and a cylindrical thrust memberthat is rotated integrally with the hub, wherein the hub has a stepportion on an inner portion of the hub, wherein a top portion of thethrust member is partially affixed to the step portion of the hub in theaxial direction, wherein a part of the top portion of the thrust membernot partially affixed axially faces at least part of the flange, whereinthe supporting member has an inner member that surrounds the shaft andan outer member that surrounds the inner member, wherein the outermember is fixed to the base member, wherein the flange is provided atthe hub side edge of the inner member, the inner member being formedseparately from the outer member, wherein the outer member is formedfrom a metallic material, and wherein the base member is formed from analuminum sheet or a steel plate.
 8. The disk drive device according toclaim 7, wherein the hub has a descending portion that axially extendstowards the base member and that annularly surrounds part of thesupporting member within the inner portion of the hub, wherein thethrust member is affixed with an adhesive to the inner portion of thehub along the descending portion of the hub, so as to allow the thrustmember to rotate with the shaft, and wherein a base side edge of thethrust member is formed so as to protrude beyond the descending portionof the hub in the axial direction.
 9. The disk drive device according toclaim 7, wherein the base member has an ascending portion that axiallyextends towards the hub and that annularly surrounds part of thesupporting member within the inner portion of the hub, wherein thesupporting member and the ascending portion form an annular area, andwherein the base side edge of the thrust member is rotated in theannular area.
 10. The disk drive device according to claim 7, whereinthe hub is formed of a stainless material having magnetism.
 11. The diskdrive device according to claim 7, wherein a diameter of the shaft is2.5 mm or less.
 12. The disk drive device according to claim 7, whereinthe hub has an annular portion and a protruded pedestal portion formedat a position spaced apart from the annular portion in the centraldirection of the hub, and fixes a magnet with the pedestal portion andthe inner circumferential surface of the annular portion.
 13. A diskdrive device comprising: a hub on which a recording disk is to bemounted; an inner member that surrounds an axis of rotation of the hub,and that has a flange radially extending outward at the hub side edge;an outer member that surrounds the inner member; a base member thatsupports the inner member and the outer member; and a cylindrical thrustmember that is rotated integrally with the hub, wherein the hub has adescending portion that axially extends towards the base member, whereinthe thrust member is affixed to an inner surface of the descendingportion of the hub, wherein a part of the top portion of the thrustmember axially faces at least part of the flange, wherein the outermember is fixed to the base member, wherein the outer member has acylindrical portion and a bottom portion, the two portions beingintegrally formed, wherein the outer member is formed from a metallicmaterial, wherein the bottom portion is provided to the base member sideedge of the cylindrical portion, wherein the hub has an annular portion,and fixes a magnet with an inner circumferential surface of the annularportion, wherein the thrust member is provided away from the magnet,wherein the flange and the outer member form an annular area, andwherein a part of the thrust member is rotated in the annular area. 14.The disk drive device according to claim 13, wherein the descendingportion annularly surrounds part of the inner member within the innerportion of the hub, wherein the thrust member is affixed with anadhesive to the inner portion of the hub along the descending portion ofthe hub, and wherein a base side edge of the thrust member is formed soas to protrude beyond the descending portion of the hub in the axialdirection.
 15. The disk drive device according to claim 13, wherein thehub has a protruded pedestal portion formed at a position spaced apartfrom the annular portion in the central direction of the hub, and fixesthe magnet with the pedestal portion.
 16. The disk drive deviceaccording to claim 13, wherein the hub is formed of a stainless materialhaving magnetism.
 17. The disk drive device according to claim 13,wherein a thrust dynamic pressure groove is formed on a surface of thethrust member, the surface facing the outer member in the axialdirection.
 18. The disk drive device according to claim 13, wherein athrust dynamic pressure groove is formed on a surface of the thrustmember, the surface facing the flange in the axial direction.
 19. Thedisk drive device according to claim 13, wherein the hub has a fittingportion into which the central holes of the recording disk is fitted,wherein the magnet overlaps the fitting portion in the axial direction.